I saw these functions in some projects. For example: in Dagon (https://gecko0307.github.io/dagon/) there are functions like onKeyDown. This function doesn't need to call - it checks pressed keys every time. Or Update in Unity (game engine). It doesn't need to call, but it executes itself every frame.

Okay, maybe it sounds confusing. I just want to understand how to implement functions that wait for events and execute code inside the function. Something like this:

void onKeyPressed(int key) {
    //the code to be executed if a key has been pressed
}

On Thursday, 28 January 2021 at 17:10:57 UTC, dog2002 wrote:
> I saw these functions in some projects. For example: in Dagon (https://gecko0307.github.io/dagon/) there are functions like onKeyDown. This function doesn't need to call - it checks pressed keys every time. Or Update in Unity (game engine). It doesn't need to call, but it executes itself every frame.
>
> Okay, maybe it sounds confusing. I just want to understand how to implement functions that wait for events and execute code inside the function. Something like this:
>
> void onKeyPressed(int key) {
>     //the code to be executed if a key has been pressed
> }

Not 100% sure what you mean but I guess you ask how to implement a handler? If an event occurs, a routine decides to call your onKeyPressed function and pass the keyCode which was pressed. The routine must be registered on a event source that will emit the events. The routine is basically just a callback and that is indeed called every frame again if an event occurs.

On Thursday, 28 January 2021 at 18:27:09 UTC, frame wrote:

> Not 100% sure what you mean but I guess you ask how to implement a handler? If an event occurs, a routine decides to call your onKeyPressed function and pass the keyCode which was pressed. The routine must be registered on a event source that will emit the events. The routine is basically just a callback and that is indeed called every frame again if an event occurs.

A very simple example:

bool myEventA = true;
bool myEventB = false;

// event source that generates the event (must be called to run)
void source() {
    observe(myEventA);
}

// routine that decides what handler to call
void observe(bool event) {
    switch (event) {
    case true:
        onMyEventA(event);
        break;

    case false:
        onMyEventB(event);
        break;

    default:
        assert(0);
    }
}

// handler
void onMyEventA(bool event) {
    // do something
}

void onMyEventB(bool event) {
    // do something
}

On Thursday, 28 January 2021 at 18:56:15 UTC, frame wrote:
> On Thursday, 28 January 2021 at 18:27:09 UTC, frame wrote:
>
>> [...]
>
> A very simple example:
>
> bool myEventA = true;
> bool myEventB = false;
>
> // event source that generates the event (must be called to run)
> void source() {
>     observe(myEventA);
> }
>
> // routine that decides what handler to call
> void observe(bool event) {
>     switch (event) {
>     case true:
>         onMyEventA(event);
>         break;
>
>     case false:
>         onMyEventB(event);
>         break;
>
>     default:
>         assert(0);
>     }
> }
>
> // handler
> void onMyEventA(bool event) {
>     // do something
> }
>
> void onMyEventB(bool event) {
>     // do something
> }

Thank you, I'll try it